1. Field of the Invention
The present invention relates to an apparatus used during orthopedic surgery, more particularly, to an instrument used to position an implant during orthopedic spine surgery.
2. Prior Art
In the field of orthopedic surgical procedures, implanting devices that can support bone or tissue to correct deformities or that will position bone and tissue in such a way as to promote healing are well known. In one such procedure, a plurality of fixation elements, such as a pedicle screw, is first positioned within the spine area. Typically, the pedicle screw is first threaded into a pedicle or other portion of vertebral bone in a vertical alignment along a segment of the spinal column. A rod is then positioned between adjoining fixation elements forming an interconnection therebetween. The combination of rods and fixation elements provides structural support to the spine area.
This same procedure is commonly performed to correct spinal degradation in addition to providing structural support to the spine area. Spinal degradation results in the loss of height between the vertebrae. This loss in height usually results in the pinching of a nerve which routes through the vertebrae, causing pain. In these cases it is often desirable to restore the spacing between the vertebrae. The series of fixation elements and rods are positioned in such a manner as to return the spacing between vertebrae therefore providing pain relief from the compressed nerve.
The spine is comprised of vertebral bones, many of which are not aligned in the same plane. Many times vertebrae are positioned at different elevations and alignments within the body, and as such create complications in establishing proper rod alignment. The process by which a rod is interconnected between two fixation elements is referred to as “rod reduction”. During the procedure, the ends of the rod are positioned within channels of opposing fixation elements. Once the ends of the rod are seated within the channels, a setscrew is positioned over the channel, securing the rod therewithin. This procedure is repeated until the desired spine area is secured.
Rod reduction is commonly performed using tools such as pliers or levers to create the necessary pushing and pulling forces that engage the rod with the implant screw. In many cases, a surgeon uses his hands to reduce the rod. In either case, however, neither the use of pliers or levers nor the use of one's hands is optimal. Pliers for example, are prone to slippage and could easily damage adjacent tissue or bone, particularly when trying to align a rod within pedicle screws, which are at different elevations or angulations. One's hands may not impart the appropriate forces required to achieve efficacious rod reduction.
Other instruments were developed to overcome the above noted issues. One such instrument, referred to as a “rocker”, is an introducer lever, which resembles a fork with a pair of offset tines. The tines are intended to extend over the suspended rod and under either side of the fixation element. Once in place, the fork handle is rotated toward the rod, thereby forcing the rod and fixation element together. This prior art design requires that the fork tines pass between the fixation element and bone. However, use of a prior art introducer lever device has not proven advantageous, as the fork tines can be prone not to securely engage with the fixation element. As such, these prior art rocker tools may slip during rod reduction, thereby causing possible injury to the patient. Additionally, passing the fork tines between the fixation element and bone may not be possible due to anatomic restrictions. Use of this prior art design also does not resolve slippage issues similar to that observed with pliers and thus may also result in damage to bone or tissue.
Other variations of these devices, commonly referred to as “forceps rockers”, have been developed to provide a more secure engagement with the fixation element. However, many of these prior art forceps rocker devices require the use of an additional instrument in concert with the forceps to reduce the rod within the fixation element. Therefore, use of these devices requires utilization of both hands, which prohibits the surgeon from manipulating another device.
Still other prior art devices such as the instrument described in U.S. Pat. No. 5,423,855 to Marienne, have been developed to provide a more secure engagement with the fixation element. The Marienne device comprises a gripping nose with articulating arms that are held in a closed position by a spring biased cap. With this type of prior design, the operator must first open the forceps to pass the mechanism over the head of the fixation element. This design was an improvement over other prior designs with regards to adapting to various anatomic constraints, however, the design does not provide adequate strength to hold the fixation element while reducing the rod, particularly when greater torques are required to properly position the rod between fixation pedicle screws.
Therefore, there is a need for an improved rocker mechanism that is easy to use, is more secure and reduces patient, bone and tissue injury risks. The present invention satisfies these needs and overcomes the problems associated with the prior art. The present invention provides an open position, which allows the device to easily slip over the head of the fixation device. Furthermore, since the present invention provides a more secure engagement with the fixation element, it is capable of generating greater torques in a single hand held instrument. In addition, the present invention provides a slender design that is less invasive and provides improved line of sight during the surgical procedure.